The present invention relates to a method for preparing a band pass signal and, in particular, to a method for preparing an analog band pass signal received from an intermediate frequency position for various transmission conditions.
German patent document DE 40 26 477 A1 discloses a method for forming a frequency multiplex signal (FDM) with digital signal processing, such as an analog band pass signal, which is preferably a modulated TV signal which can be displayed, received, and processed in a intermediate frequency position. The received band pass signal is converted via an analog/digital converter into a digital band pass signal and further converted for further processing into a corresponding digitally filtered and frequency adjusted condition. Several such types of prepared digital band pass signals are converted into the frequency in a manner such that they are coupled with one another in a frequency domain in an overlapping free manner and are combined into a frequency multiplex signal through digital addition. For a selected or predetermined receipt frequency, the middle frequency of the band pass signals must be set and maintained in a narrow tolerance range since the receipt frequency is chosen as the minimum reliable value in accordance with signal receipt theory. As a result, the processing rate in the digital frequency conversion apparatus is relatively low; in contrast, however, the total work in the realization of this processing rate is relatively high due to the small transfer region of the analog pre filter (especially an anti-alias filter) and the digital filter. In a further configuration of this processing rate as disclosed in German patent document DE 43 37 134 A1, a doubled sampling frequency is processed and this leads to the following advantages: --all of the filter demands are eliminated (analog and digital), -the neighboring channel selection (the immediately neighboring channel) does not need to be implemented via the tolerance restricted analog anti-alias filter but, rather, via a robust digital deep pass filter, --the band middle frequency of the band pass signal to be processed is the same as a standard intermediate frequency position such as, for example, a European norm with the image carrier of 38.9 Hz, and even cost favorable standard ZF filters can be used as the anti-alias filter in advance of the analog/digital conversion.